In a photolithography process for manufacturing semiconductor devices and liquid crystal displays (LCD's), resist is coated on a substrate, and the resultant photoresist coating film is exposed to light and developed. The series of processing stages are carried out in a coating/developing processing system having discrete heating sections, such as a prebaking unit and a postbaking unit. Each heating section incorporates a hotplate with a built-in heater of a resistance heating type.
Feature sizes of semiconductor device circuits have been reduced to less than 0.1 microns. Typically, the pattern wiring that interconnects individual device circuits is formed with sub-micron line widths. To provide reproducible and accurate feature sizes and line widths, it has been strongly desired to control more accurately light exposure parameters and the heat treatment temperature of the photoresist film. The substrates or wafers (i.e., objects to be treated) are usually treated or processed under the same recipe (i.e., individual treatment program) in units (i.e., lots) each consisting of, for example, twenty-five wafers. Individual recipes define heat treatment conditions under which prebaking and postbaking are performed. Wafers belonging to the same lot are heated under the same conditions.
Heat-treating a photoresist plays an important role in the photoresist processing and may have many purposes, from removing a solvent from the photoresist to catalyzing chemical amplification in the photoresist. In addition to the intended results, heat-treating may cause numerous problems. For example, the light sensitive component of the photoresist may decompose at temperatures typically used to remove the solvent, which is an extremely serious concern for a chemically amplified resist (CAR) since the remaining solvent content has a strong impact on the diffusion and amplification rates. Also, heat-treating can affect the dissolution properties of the resist and thus have direct influence on the developed resist profile. CAR's are particularly sensitive to temperature variations during heat treatment and temperature variations can result in variations in critical dimensions (CDs) across a wafer surface.
Therefore, real time metrology data collection of physical properties of processed resist coated wafers is required in order to optimize light exposure parameters and the temperature profile across the wafers in the heat-treating process. New methods are needed that provide the high metrology data density required for controlling and optimizing the light exposure and heat-treating process, while allowing for high wafer throughput.